CCL: What is the meaning of minus value of Mulliken atomic spin densities?

 Sent to CCL by: Marcel Swart [marcel.swart]=[icrea.es]
 First, much depends on the spin polarization that you have given,
 i.e. in case of a doublet, if this doublet spin density should be
 in the alpha spins, or in the beta spins.
 (10 alpha 9 beta, vs. 9 alpha 10 beta)
 In principle, the sign of the spin densities should depend on
 this choice.
 Second, it depends if the program takes into account the electric
 charge for an electron or not. I.e. again looking at the 10alpha-9beta
 system, the total number of spin-polarized alpha-beta electrons is +1,
 with a corresponding total charge of -1. I'm almost certain that most
 programs report the -1 (charge) and not the number (+1), but I'm not
 sure.
 Third, Mulliken charges are known to be very basis set sensitive.
 Anyone of these factors influences your system, and even more so
 when you have a (transition) metal present.
 Marcel
 On Aug 13, 2010, at 1:48 PM, wangzc^iccas.ac.cn wrote:
 > Dear all,
 >
 >     Recently I calculated a structure with MINUS value of Mulliken atomic
 spin densities,anyone can tell me how to understand that minus value?
 >
 >     Thanks very much!
 ===================================
 dr. Marcel Swart
 ICREA Research Professor at
 Institut de Química Computacional
 Universitat de Girona
 Parc Científic i Tecnològic
 Edifici Jaume Casademont (despatx A-27)
 Pic de Peguera 15
 17003 Girona
 Catalunya (Spain)
 tel
 +34-972-183240
 fax
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 marcel.swart!^!icrea.es
 marcel.swart!^!udg.edu
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